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Satellites organized in flexible networks known as constellations are more agile and resilient than are those operating alone. Manoeuvring satellites into such constellations requires inexpensive, reliable and efficient engines. Many networked satellites have electric propulsion thrusters, which generate thrust by using electrical energy to accelerate the ions of a propellant gas. However, the choice of gas presents a problem. Ionizing xenon requires a relatively small amount of energy, but xenon gas is expensive and needs to be compressed in high-pressure tanks to fit on board a satellite. Krypton is cheaper, but still requires a complex and heavy gas-storage and -supply system. Writing in Nature, Rafalskyi et al.1 report a successful demonstration of an iodine-ion thruster in space — offering a cheaper and simpler alternative to xenon or krypton.